1. Field of the Invention
The present invention relates to a thermoelectric conversion module for use in an apparatus utilizing a thermoelectric effect such as an electronic cooling apparatus and an electric power generating apparatus, and more particularly to a thermoelectric conversion module having N type semiconductor elements and P type semiconductor element connected in cascade or in series by means of metal electrodes. The present invention also relates to a method of manufacturing such a thermoelectric conversion module.
2. Related Art Statement
There have been proposed various kinds of thermoelectric conversion modules utilizing the Seebeck effect, Peltier effect and Thomson effect. Among these thermoelectric conversion modules, there have been realized a Seebeck effect element and Peltier effect element, in which a thermoelectric element is formed by joining different kinds of metals. In the Seebeck effect element, different kinds of metals are joined to constitute a closed loop, and thermoelectricity is generated by making junctions at different temperatures. Such a Seebeck effect element may be utilized as a thermoelectric element. In the Peltier effect element, different kinds of metals are joined to form a closed loop and an electric current is passed through the loop in a given direction to cause heat absorption at one junction point and heat generation at the other junction point. Such a thermoelectric element may be utilized as a thermoelectric heating element or thermoelectric cooling element. In order to improve an efficiency of these elements, a junction between a semiconductor and a metal has been widely used.
FIG. 1 is a schematic view showing a principal structure of a known thermoelectric conversion module constructed as the above mentioned thermoelectric element. The thermoelectric conversion module comprises a number of N type semiconductor elements 1 and a number of P type semiconductor elements 2, said N and P type semiconductor elements being arranged alternately. Adjacent N type and P type semiconductor elements 1 and 2 are connected in series by means of electrodes 3 made by metal segments. The left side N type semiconductor element 1 and the right side P type semiconductor element 2 of the series connection semiconductor element array are connected to opposite ends of a load 4. One side of the semiconductor array is placed in a higher temperature environment and the other side is placed in a lower temperature environment. Then, in each of the N type semiconductor elements 1, electrons flow from the high temperature side to the low temperature side as shown by solid lines. In each of the P type semiconductor elements 2, holes flow from the high temperature side to the low temperature side as depicted by broken lines. Therefore, a voltage is applied across the load 4 with a polarity depicted in FIG. 1. The semiconductor elements 1 and 2 may be made of Bi--Te semiconductor (for instance Bi.sub.2 Te.sub.3), Bi--Sb semiconductor (for example Bi.sub.0.88 Sb.sub.0.12) or Si--Ge (for instance Si.sub.0.8 Ge.sub.0.2).
FIG. 2 is a perspective view showing a known method of manufacturing the above mentioned known thermoelectric conversion module. On a surface of an insulating substrate 5 are secured electrode metal strips 6 by brazing in accordance with a given pattern. Then, N type semiconductor elements 1 and P type semiconductor elements 2 are secured to the metal segments 6 by brazing or soldering. The semiconductor elements 1 and 2 may be formed by a single crystal melting method or a sintered semiconductor material cutting method. On upper surfaces of the N type and P type semiconductor elements 1 and 2 there are secured metal Segments 7 by means of brazing or soldering. In this manner, the N type semiconductor elements 1 and P type semiconductor elements 2 are arranged alternately and are connected in series by means of the metal segments 6 and 7. In this case, it has been proposed to secure the metal segments 7 simultaneously to the semiconductor elements 1 and 2 by using an insulating plate on which a metal electrode pattern is previously formed.
In Japanese Patent Publication No. 6-9260 (JP 6-9260), there is disclosed a known method of manufacturing a thermoelectric conversion module, in which a molten or fused semiconductor material is sucked into a thin quartz or glass tube having a size of 7.PHI..times.5.PHI..times.600 mm by means of a sucking tool, and after cooling the semiconductor material melt, the tube is cut into pieces having a given length. Then, these tubes are arranged side by side.
In Japanese Patent Laid-open Publication Kokai Hei 5-315656 (JP 5-315656), there is proposed another known method of manufacturing a thermoelectric conversion module, in which a molten thermoelectric material is poured into holes formed in an electrically insulating substrate made of a heat resistant material. In this method, the mechanical strength of the module is reinforced by the substrate, while a superior property of one direction solidified material is maintained.
If a large capacity thermoelectric conversion module including a large number of thermoelectric elements is to be manufactured by the first mentioned known method, extremely high working precision and high assembling faculty are required, and thus a manufacturing cost will be increased very much. Moreover, it is impossible to manufacture a thermoelectric conversion module having a curved surface. Such a curved surface is required when a thermoelectric conversion module is secured to a base member having a curved surface. In this manner, the module made by this known method could not be used in various applications. For instance, when the thermoelectric conversion module is applied to a system in which electric power is generated by using waste heat of an internal combustion engine, a space for providing the thermoelectric conversion module is limited and in many cases it is desired to provide the thermoelectric conversion module on a curved surface. However, the module made by the above mentioned known method could not have a curved surface, and therefore could not be applied to such a thermoelectric power system.
In the known method described in JP 6-9260, the sucking tool has various problems in reliability, durability and cost. Moreover, this known method requires a rather complicated process. Also in this method it is impossible or at least very difficult to manufacture a thermoelectric conversion module having a curved surface.
In the known method disclosed in JP 5-315656, a molten thermoelectric material could be uniformly introduced into holes formed in the insulating substrate only with difficulty. This method is not also suitable for obtaining a thermoelectric conversion module having a curved surface.